1) Field of the Invention
The present invention relates to the field of medical instruments. It more particularly concerns a hand-held instrument designed to rotate, at a high speed, a detachable rectilinear tool whereof the end constitutes a bur or similar member usable in dental offices or laboratories as well as in microsurgery.
2) Description of Related Art
One instrument of this type is described, for example, in document WO 2005/089666. Typically, the shank of the tool is held by a clamp arranged inside a hollow rotating shaft driven at its end by an electric motor or an air turbine and mounted by bearings in a fixed tubular sheath. Gripping and releasing of the clamp is done by turning a sleeve mounted to rotate on the shaft in one direction or the other.
In order to facilitate vision of the operation area, hand-held instruments intended for dental or microsurgical use obviously require a long, slender nose. This type of restriction unfortunately limits the possibility of ensuring good guiding of the tool at the end of the nose by means of a very small and sufficiently resistant bearing.
The shank of the tool, the diameter of which is generally only 2.35 mm, having a limited stiffness and being able to have an “out-of-round”, the clamp which ensures its gripping therefore risks forcing it somewhat, which causes it to bow and the active end of the tool to oscillate. One will easily understand that this untimely shaking is very damaging to the precision of the bur's action.
The present invention aims in particular to provide an instrument wherein the noise and vibrations resulting from imperfect gripping and guiding of the shank of the tool are very greatly reduced, or even eliminated. The invention also aims to stress the ball bearing less and thereby to improve its lifespan.